1. Field of the Invention
The present invention relates to a flow improver for biodiesel fuels that can improve low temperature stability in relation to a cold filter plugging point (hereinafter referred to plugging point), a pour point, or the like. The present invention relates also to a biodiesel fuel composition with excellent low temperature stability.
2. Background Art
In recent years, due to concern over depletion of fossil fuels such as petroleum and coal, the effective utilization of natural energy like solar light, wind power, and hydraulic power, and of biomass fuels derived from animals and plants is being tested. Furthermore, particular focus is being given to plant-based biomass fuels due to their contribution to carbon dioxide reduction on a global scale. In the case of plant-based biomass fuels, plants are processed and used as a source of carbon. Thus, because the carbon dioxide emitted by plants and trees is again absorbed by plants and trees due to photosynthesis and is cycled, it is considered that it does not affect the carbon dioxide concentration at the global level. Such fuels have a status of carbon neutral fuels.
Plant-based biomass fuels, such as ethanol obtained by fermenting sugarcane and whole grains like corn, and ethyl tertiary butyl ether obtained by reacting ethanol and isobutene are being examined as alternative fuels for use in gasoline-powered vehicles.
On the other hand, fuels using animal and plant-based fats and oils as basic ingredients, also known as biodiesel fuels, are generally used as biomass fuel in diesel vehicles. Since the animal and plant-based fats and oils have a high boiling point and high viscosity, they are not adapted for use without modification in the form of diesel fuel. Therefore, a biodiesel fuel includes animal and plant-based fats and oils that are processed and converted to a fuel having physical properties, such as a boiling point range and viscosity, that are close to the physical properties of light diesel oil.
The most commonly used components are fatty acid esters such as fatty acid methyl ester and fatty acid ethyl ester, which are derived from animal and plant-based fats and oils. However, compared to light diesel oils, biodiesel fuels made from fatty acid esters, such as fatty acid methyl ester and fatty acid ethyl ester tend to have reduced stability at low temperatures. Since fatty acid esters obtained from animal and plant-based oils and fats possess fatty acid distribution derived from the oils and fats used as the raw material, they have various low-temperature characteristics, such as a plugging point and a pour point. Generally, biodiesel fuels containing a large amount of saturated fatty acid methyl ester and saturated fatty acid ethyl ester manufactured by using fats and oils with a high content of saturated fatty acids as the raw material have reduced stability at low temperatures and declined flow characteristics. Therefore, the period and place of their usage are restricted.
However, with reference to the current energy situation, there is a need to use fatty acid esters, such as fatty acid methyl ester and fatty acid ethyl ester obtained by using various fats and oils as the raw material, and from the viewpoint of economic efficiency and supply stability, even the use of fatty acid esters with poor stability at low temperatures that use fats and oils with a high content of saturated fatty acids as the raw material is being widely examined.
On the other hand, flow improvers for middle distillates that are used in middle distillates such as light diesel oil and heavy fuel oil A are known to have almost no effect when used on fatty acid esters without modification. In light of this situation, various low temperature flow improvers have been disclosed as a flow improver for middle distillates to enable use of biodiesel fuels by improving the stability of fatty acid esters at low temperatures. For example, Patent Literature 1 discloses that a mixture of esters of polymers and copolymers of acrylic and/or methacrylic acids and alcohols containing from 1 to 22 carbon atoms can improve the low temperature stability of fatty acid methyl ester. Moreover, Patent Literature 2 discloses an additive for biodiesel fuels formed from a copolymer of alkyl methacrylate containing 8 to 30 carbon atoms in the alkyl group, polyoxyalkylene alkyl methacrylate containing 1 to 20 carbon atoms in the alkyl group, and alkyl methacrylate containing 1 to 4 carbon atoms in the alkyl group. Furthermore, Patent Literature 3 discloses a low temperature flow improver for methyl ester of animal or plant origin formed from an ethylene-vinyl ester copolymer containing 17 mole percent or more of vinyl ester unit and also containing five or more alkyl branches for every 100 units of methylene in the main chain.
However, in spite of the fact that low temperature flow improvers using such copolymers exhibited an improvement in fluidity at low temperatures for some fatty acid esters, they were not sufficient for fatty acid esters with different types of fatty acid compositions, particularly fatty acid esters with a high content of saturated fatty acid esters. Therefore, there is a need for a flow improver for biodiesel fuels with excellent stability improvement effect at low temperatures for fatty acid esters with various fatty acid compositions.
Citation List
Patent Literature
    [Patent Literature 1] European Patent No. 0563070    [Patent Literature 2] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2001-524578    [Patent Literature 3] Japanese Unexamined Patent Application Publication No. 2005-015798